BLACKNESS

, the quality of a black body, as to
colour; arising from its stifling or absorbing the rays of
light, and reflecting little or none. In which sense it
stands directly opposed to whiteness; which consists in
such a texture of parts, as indifferently reflects all the
rays thrown upon it, of whatever colour they may be,

Descartes, it seems, first rightly distinguished these
causes of black and white, though he might be mistaken
with respect to the general nature of light and colours.
—Sir lsaac Newton shews, in his Optics, that to produce
black colours, the corpuscles must be smaller than
for exhibiting the other colours; because, where the
sizes of the component particles of a body are greater,
the light reflected is too much for constituting this colour:
but when they are a little smaller than is requisite
to reflect the white, and very faint blue of the first
order, they will reflect so little light, as to appear intensely
black; and yet they may perhaps reflect it
variously to and fro within them so long, till it be stifled
and lost.

And hence, it appears, why fire, or putrefaction,
by dividing the particles of substances, turn them black:
why small quantities of black substances impart their
colours very freely, and intensely, to other substances,
to which they are applied; the minute particles of these,
on account of their very great number, easily overspreading
the gross particles of others. Hence it also appears,
why glass ground very elaborately on a copper-plate
with sand, till it be well polished, makes the sand, with
what is rubbed off from the copper and glass, become
very black: also why blacks commonly incline a little
towards a blueish colour; as may be seen by illuminating
white paper with light reflected from black substances,
when the paper usually appears of a blueish white; the
reason of which is, that black borders on the obscure
blue of the first order of colours, and therefore reflects
more rays of that colour than of any other: and lastly
why black substances do sooner than others become hot
in the sun's light, and burn; an effect which may proceed
partly from the multitude of refractions in a little
space, and partly from the easy commotion among such
minute particles.

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